JP6646062B2 - Polishing agent for synthetic quartz glass substrate, method for producing the same, and method for polishing synthetic quartz glass substrate - Google Patents

Description

  The present invention relates to an abrasive for a synthetic quartz glass substrate and a method for producing the same. The present invention also relates to a method for polishing a synthetic quartz glass substrate.

  In recent years, due to miniaturization of patterns by optical lithography, stricter requirements have been placed on the quality of a synthetic quartz glass substrate such as defect density, defect size, surface roughness, and flatness. Above all, with respect to defects on a substrate, further improvement in quality is required as the definition of integrated circuits increases and the capacity of magnetic media increases.

  From such a viewpoint, in order to improve the quality of the polished quartz glass substrate, the surface roughness of the polished quartz glass substrate or the polished quartz glass It is strongly required that the surface of the substrate has few surface defects such as scratches. Further, from the viewpoint of improving productivity, a high polishing rate of the quartz glass substrate is also required.

  Conventionally, silica-based abrasives have been generally studied as abrasives for polishing synthetic quartz glass. Silica-based slurries are produced by subjecting silica particles to particle growth by thermal decomposition of silicon tetrachloride and adjusting the pH with an alkaline solution containing no alkali metal such as ammonia. For example, Patent Literature 1 describes that high purity colloidal silica can be used near neutrality to reduce defects. However, considering the isoelectric point of colloidal silica, colloidal silica is unstable in the vicinity of neutral, and there is a concern that the particle size distribution of the colloidal silica abrasive grains during polishing fluctuates and cannot be used stably. Therefore, there is a problem that it is difficult to circulate and repeatedly use the abrasive, and it is not economically preferable because the abrasive needs to be used in a flowing manner.

  Patent Document 2 discloses that defects can be reduced by using an abrasive containing colloidal silica having an average primary particle diameter of 60 nm or less and an acid. However, these abrasives are not enough to satisfy the current requirements and need to be improved.

On the other hand, ceria (CeO ₂ ) particles have a lower hardness than silica particles and alumina particles, so that defects such as scratches hardly occur on the surface of the synthetic quartz glass substrate after polishing. Therefore, an abrasive using ceria particles as abrasive grains is effective for reducing defects. Also, ceria particles are known as strong oxidizing agents and have chemically active properties, so that ceria-based abrasives are effective for application to polishing of inorganic insulators such as glass.

  However, in general, ceria-based abrasives use dry ceria particles, and since dry ceria particles have an amorphous crystal shape, they have a high polishing efficiency, but when dry ceria is applied to the abrasive, a quartz glass substrate is used. There is a problem that defects such as scratches easily occur on the surface. On the other hand, wet ceria particles have a more stable polyhedral structure than dry ceria particles. Thereby, defects such as scratches can be significantly reduced as compared with conventional dry ceria particles, and wet ceria particles are useful as abrasive grains.

JP-A-2004-98278 JP 2007-213020 A JP 2006-167817 A

  However, when only wet ceria particles are used as polishing abrasive grains, defects such as scratches are sufficiently reduced, but the polishing rate does not satisfy the polishing rate currently required. For example, Patent Document 3 describes that a polishing rate can be increased by adding a polymer having a sulfonic acid group such as an acrylic acid / sulfonic acid copolymer to an abrasive using colloidal silica and using the same. Have been. However, even if such a polymer is added to a ceria-based polishing agent, it does not satisfy the polishing rate required at present, and it is necessary to further improve the polishing rate. As described above, the conventional technique has a problem that it is difficult to achieve both reduction of polishing defects and sufficient improvement of the polishing rate.

  The present invention has been made in view of the above-described problems, and has an object to provide an abrasive for a synthetic quartz glass substrate having a high polishing rate and capable of sufficiently reducing the occurrence of defects due to polishing. I do. Another object of the present invention is to provide a method for producing an abrasive for a synthetic quartz glass substrate capable of producing such an abrasive for a synthetic quartz glass substrate. Still another object of the present invention is to provide a method for polishing a synthetic quartz glass substrate having a high polishing rate and capable of sufficiently reducing the generation of defects.

  In order to achieve the above object, the present invention is an abrasive for a synthetic quartz glass substrate containing abrasive particles and water, wherein the abrasive particles comprise mixed abrasive particles of wet ceria particles and dry ceria particles, An abrasive for a synthetic quartz glass substrate, characterized in that the mass ratio between wet ceria particles and dry ceria particles is 70/30 or more and 90/10 or less.

  The abrasive for a synthetic quartz glass substrate of the present invention (hereinafter, also simply referred to as "abrasive") is used for wet ceria particles capable of reducing the occurrence of defects such as scratches during polishing of the synthetic quartz glass substrate, and for the synthetic quartz glass substrate. Since dry ceria particles having a high polishing efficiency include mixed abrasive particles mixed in the above ratio, in polishing using this abrasive, defects such as scratches are unlikely to occur on the surface of the synthetic quartz glass substrate, A sufficiently high polishing rate can be obtained.

  At this time, it is preferable that the average primary particle diameter of the wet ceria particles is 40 nm or more and 100 nm or less, and the average primary particle diameter of the dry ceria particles is 100 nm or more and 300 nm or less.

  Thus, when the average primary particle diameter of the wet ceria particles is 40 nm or more and the average primary particle diameter of the dry ceria particles is 100 nm or more, a higher polishing rate can be obtained. Further, when the average primary particle diameter of the wet ceria particles is 100 nm or less and the average primary particle diameter of the dry ceria particles is 300 nm or less, generation of polishing scratches such as scratches can be further suppressed.

  The abrasive of the present invention preferably has a concentration of the mixed abrasive particles of 5 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the synthetic quartz glass substrate abrasive.

  When the concentration of the mixed abrasive particles is 5 parts by mass or more with respect to 100 parts by mass of the abrasive for a synthetic quartz glass substrate, the abrasive of the present invention can obtain a higher polishing rate. When the concentration of the mixed abrasive particles is 40 parts by mass or less with respect to 100 parts by mass of the abrasive for a synthetic quartz glass substrate, the storage stability of the abrasive is further improved.

  Further, the abrasive of the present invention further contains an additive, and the concentration of the additive is preferably 0.1 part by mass or more and 5 parts by mass or less based on 100 parts by mass of the mixed abrasive particles.

  The abrasive of the present invention may contain an additive for the purpose of adjusting the polishing characteristics. If the concentration is 0.1 parts by mass or more with respect to 100 parts by mass of the mixed abrasive particles, the effect of adjusting the polishing characteristics is obtained. Is sufficiently obtained. When the concentration of the additive is 5 parts by mass or less with respect to 100 parts by mass of the mixed abrasive particles, the additive does not hinder polishing, and a reduction in polishing rate can be prevented.

  In addition, the abrasive of the present invention preferably has a pH of 3.0 or more and 8.0 or less.

  When the pH is 3.0 or more, wet ceria in the abrasive is stably dispersed, and secondary particles having a large particle diameter are not easily generated. When the pH is 8.0 or less, the polishing rate can be further improved.

  Further, in order to achieve the above object, the present invention provides a method for polishing a synthetic quartz glass substrate having a rough polishing step and a finish polishing step after the rough polishing step. Provided is a method for polishing a synthetic quartz glass substrate, characterized in that finish polishing is performed using an abrasive for a glass substrate.

  With such a polishing method using the abrasive of the present invention, the polishing rate can be increased and the generation of defects due to polishing can be suppressed. In addition, the polishing method of the present invention can obtain a synthetic quartz glass substrate having significantly less defects, and thus can be suitably used for finish polishing.

  Further, in order to achieve the above object, the present invention is a method for producing an abrasive for a synthetic quartz glass substrate, wherein a step of producing wet ceria particles, a step of producing dry ceria particles, and the wet ceria particles Mixing the wet ceria particles, the wet ceria particles, and water so that the mass ratio of the dry ceria particles is 70/30 or more and 90/10 or less. Provided is a method for producing an abrasive.

  This makes it possible to produce an abrasive for a synthetic quartz glass substrate that is less likely to cause defects such as scratches on the surface of the synthetic quartz glass substrate and that can obtain a sufficiently high polishing rate.

  At this time, in the wet ceria particle producing step, a mixed solution is prepared by mixing a cerium salt and a basic solution, and the wet ceria particles are produced by a wet chemical precipitation reaction by heating the mixed solution. be able to.

  Further, in the dry ceria particle producing step, the dry ceria particles can be produced by a solid phase substitution reaction by firing a cerium salt in the presence of oxygen.

  In the method for producing an abrasive for a synthetic quartz glass substrate of the present invention, wet ceria particles and dry ceria particles can each be suitably produced by the above-described method.

  With the abrasive of the present invention, it is possible to obtain a sufficient polishing rate in polishing a synthetic quartz glass substrate and sufficiently suppress the generation of defects on the surface of the synthetic quartz glass substrate. As a result, productivity and yield in the production of a synthetic quartz glass substrate can be improved. In addition, in particular, by using the abrasive for a synthetic quartz glass substrate of the present invention in the finishing polishing step in the manufacturing process of the synthetic quartz glass substrate, a high-quality synthetic quartz glass substrate can be obtained, and as a result, a semiconductor device Leads to higher definition.

5 is a photograph of wet ceria particles produced by a wet chemical precipitation method. 4 is a photograph of dry ceria particles produced by a solid phase replacement method. FIG. 2 is a schematic view showing an example of a polishing apparatus that can be used in the method for polishing a synthetic quartz glass substrate of the present invention.

  Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

  As described above, the abrasive for synthetic quartz glass substrates of the present invention (hereinafter, also simply referred to as “abrasive”) has abrasive particles composed of mixed abrasive particles of wet ceria particles and dry ceria particles, and wet ceria particles. And dry ceria particles in a mass ratio of 70/30 or more and 90/10 or less.

  Wet ceria particles have lower hardness than silica particles and alumina particles, and have a more stable polyhedral structure than dry ceria particles. The abrasive for synthetic quartz glass substrates of the present invention can suppress generation of defects such as scratches due to polishing by using such abrasive grains mainly composed of wet ceria particles. In addition, the abrasive of the present invention further includes dry ceria particles in the above-mentioned mass ratio smaller than that of wet ceria particles, so that even when wet wet ceria particles are used as abrasive grains, sufficiently high polishing is achieved. You can get speed. Dry ceria particles have an irregular polycrystalline structure unlike wet ceria particles. Therefore, it has a higher active surface than a wet ceria particle having a stable single crystal structure. Therefore, it is presumed that a chemical reaction easily occurs between the dry ceria particles and the surface of the synthetic quartz glass substrate in the polishing process, and as a result, polishing is promoted by modifying the surface of the synthetic quartz glass.

  Hereinafter, each component of the polishing agent of the present invention, components that can be optionally added to the polishing agent of the present invention, a method for producing the polishing agent of the present invention, and a method for polishing a synthetic quartz glass substrate will be described in more detail.

  As described above, as abrasive particles contained in the abrasive of the present invention, mixed abrasive particles obtained by mixing wet ceria particles and dry ceria particles are used. Wet ceria particles are preferred in that particles having a large secondary particle size are unlikely to be generated, and have a polyhedral structure, and can improve polishing scratches such as scratches. On the other hand, dry ceria particles have an amorphous polycrystalline structure and therefore have a lower effect of improving polishing flaws than wet ceria particles, but are preferred because they have high particle activity and can achieve high polishing efficiency.

  Further, as described above, the wet ceria particles and the dry ceria particles are mixed in a mass ratio of 70/30 to 90/10. At this time, if the mixing ratio of the dry ceria particles is too high, the occurrence of polishing scratches such as scratches generated on the surface of the synthetic quartz glass substrate after polishing increases. The polishing rate cannot be obtained.

  Further, as the wet ceria particles in the abrasive of the present invention, those having an average primary particle diameter of 200 nm or less can be used. Among these, it is particularly preferable that the average primary particle diameter of the wet ceria particles is 40 nm or more and 100 nm or less. When the average primary particle diameter of the wet ceria particles is 40 nm or more, the polishing rate on the synthetic quartz glass substrate becomes higher. Less likely to occur.

  Further, as the dry ceria particles in the abrasive of the present invention, those having an average primary particle diameter of 500 nm or less can be used. Among these, the average primary particle diameter of the dry ceria particles is preferably 100 nm or more and 300 nm or less. When the average primary particle diameter of the dry ceria particles is 100 nm or more, the polishing rate on the synthetic quartz glass substrate becomes higher. Less likely to occur.

  The average primary particle diameter of the wet ceria particles and the dry ceria particles may be calculated using a circle equivalent diameter calculated by an electron microscope as an average primary particle diameter.

  The concentration of the mixed abrasive particles in the abrasive of the present invention is not particularly limited, but from the viewpoint that a suitable synthetic quartz glass substrate polishing rate can be obtained, 0.1 parts by mass relative to 100 parts by mass of the abrasive. It is preferably at least 1 part by mass, more preferably at least 1 part by mass, particularly preferably at least 5 parts by mass. In addition, the upper limit concentration of the abrasive particles is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and particularly preferably 20 parts by mass or less, from the viewpoint of increasing the storage stability of the abrasive.

  Further, the abrasive of the present invention may contain an additive for the purpose of adjusting polishing characteristics. Such additives are not particularly limited, but may include an anionic surfactant capable of converting the surface potential of the abrasive particles to a negative value, or an amino acid. If the surface potential of the ceria particles is set to a negative value, the ceria particles are easily dispersed in the abrasive, so that secondary particles having a large particle diameter are not easily generated, and the generation of polishing scratches can be further suppressed.

  Anionic surfactants as additives include monoalkyl sulfates, alkyl polyoxyethylene sulfates, alkyl benzene sulfonates, monoalkyl phosphates, lauryl sulfates, polycarboxylic acids, polyacrylates, polymethacrylates Acid salts and the like. Amino acids include, for example, arginine, lysine, aspartic acid, glutamic acid, asparagine, glutamine, histidine, proline, tyrosine, serine, tryptophan, threonine, glycine, alanine, methionine, cysteine, phenylalanine, leucine, valine, isoleucine and the like.

  When these additives are used, the concentration is preferably from 0.1 to 5 parts by mass based on 100 parts by mass of the mixed abrasive particles. When the concentration of the additive is 0.1 parts by mass or more with respect to 100 parts by mass of the mixed abrasive particles, the effect of adjusting the polishing characteristics can be sufficiently exhibited, for example, the wet ceria particles are more stable in the abrasive. To form aggregated particles having a large particle diameter. When the concentration of the additive is 5 parts by mass or less with respect to 100 parts by mass of the mixed abrasive particles, the additive does not hinder polishing, and a reduction in polishing rate can be prevented. Therefore, when the additive is included in the above range, the dispersion stability of the abrasive can be further improved, and the reduction of the polishing rate can be prevented.

  Further, the pH of the abrasive of the present invention is preferably in the range of 3.0 or more and 8.0 or less from the viewpoint of excellent storage stability and polishing rate of the abrasive. If the pH is 3.0 or more, the wet ceria in the abrasive is stably dispersed. When the pH is 8.0 or less, the polishing rate can be further improved. Further, the lower limit of the pH is more preferably 4.0 or more, and particularly preferably 6.0 or more. Further, the upper limit of the pH is preferably 8.0 or less, and more preferably 7.0 or less. In addition, the pH of the polishing agent is selected from inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid, organic acids such as formic acid, acetic acid, citric acid and oxalic acid, ammonia, sodium hydroxide, potassium hydroxide and tetramethylammonium hydroxide. It can be adjusted by adding (TMAH) or the like.

  Subsequently, a method for producing the abrasive for a synthetic quartz glass substrate of the present invention will be described. In the method for producing an abrasive according to the present invention, the step of producing wet ceria particles, the step of producing dry ceria particles, and the mass ratio of wet ceria particles to dry ceria particles become 70/30 or more and 90/10 or less. And mixing the wet ceria particles, the wet ceria particles, and water. In addition, a step of mixing an additive may be further provided.

  The method for producing an abrasive of the present invention is characterized in that in a wet ceria particle producing step, a mixed solution is prepared by mixing a cerium salt and a basic solution, and a wet chemical precipitation reaction is performed by heat-treating the mixed solution. Wet ceria particles can be produced.

  The method for producing wet ceria particles by a wet chemical precipitation reaction will be described more specifically. First, a cerium salt as a precursor is mixed with ultrapure water to produce a cerium aqueous solution. The cerium salt and ultrapure water can be mixed, for example, at a ratio of 2: 1 to 4: 1. Here, as the cerium salt, at least one of a Ce (III) salt and a Ce (IV) salt can be used. That is, at least one Ce (III) salt is mixed with ultrapure water, at least one Ce (IV) salt is mixed with ultrapure water, or at least one Ce (III) salt The salt and at least one Ce (IV) salt can be mixed with the ultrapure water. Ce (III) salts include cerium (III) chloride, cerium (III) fluoride, cerium (III) sulfate, cerium (III) nitrate, cerium (III) carbonate, cerium (III) perchlorate, cerium bromide (III), cerium (III) sulfide, cerium (III) iodide, cerium (III) oxalate, cerium (III) acetate and the like can be mixed, and the Ce (IV) salt is cerium (IV) sulfate. , Cerium (IV) ammonium nitrate, cerium (IV) hydroxide and the like can be mixed. Among them, cerium (III) nitrate is preferably used as the Ce (III) salt, and ammonium cerium (IV) nitrate is preferably used as the Ce (IV) salt in terms of ease of use.

  Further, an acidic solution can be mixed for stabilization of the cerium aqueous solution produced by mixing with ultrapure water. Here, the acidic solution and the cerium solution can be mixed at a ratio of 1: 1 to 1: 100. Examples of the acidic solution that can be used here include hydrogen peroxide, nitric acid, acetic acid, hydrochloric acid, and sulfuric acid. The pH of the cerium aqueous solution mixed with the acidic solution can be adjusted to, for example, 0.01.

  A basic solution is prepared separately from the cerium aqueous solution. As the basic solution, ammonia, sodium hydroxide, potassium hydroxide or the like can be used, and it is used after being mixed with ultrapure water and diluted to an appropriate concentration. As a dilution ratio, a basic substance and ultrapure water can be diluted at a ratio of 1: 1 to 1: 100. The pH of the diluted basic solution can be adjusted to, for example, 11 to 13.

  Next, after the diluted basic solution is transferred to the reaction vessel, stirring is performed, for example, for 5 hours or less in an atmosphere of an inert gas such as nitrogen, argon, or helium. Then, a cerium aqueous solution is mixed with the diluted basic solution at a speed of, for example, 0.1 liter per second or more. Subsequently, heat treatment is performed at a predetermined temperature. At this time, the heat treatment can be performed at a heat treatment temperature of 100 ° C. or less, for example, 60 ° C. or more and 100 ° C. or less, and the heat treatment time can be 2 hours or more, for example, 2 hours to 10 hours. Further, the temperature can be raised at a rate of 0.2 ° C. to 1 ° C. per minute, preferably 0.5 ° C. per minute, from the room temperature to the heat treatment temperature.

  Next, the heat-treated mixed solution is cooled to room temperature. Through such a process, a mixed liquid in which wet ceria particles having a primary particle diameter of, for example, 100 nm or less are produced.

As described above, the wet ceria particles are formed by heating a mixture of a cerium salt precursor aqueous solution and a diluted basic solution at an appropriate heating rate and heating the mixture at an appropriate range of heat treatment temperature. The cerium salt in the mixed solution reacts during the temperature process to generate fine nuclei of ceria (CeO ₂ ), and crystals grow around these fine nuclei, and are produced with crystal particles of 5 nm to 100 nm. . As shown in FIG. 1, the wet ceria particles thus produced have a more stable polyhedral structure than the dry ceria particles. Therefore, when used as abrasive particles, defects such as scratches can be significantly reduced as compared with dry ceria particles.

  In the method for producing an abrasive according to the present invention, in the dry ceria particle producing step, it is preferable to produce dry ceria particles by a solid phase substitution reaction by firing a cerium salt in the presence of oxygen.

  A method for producing dry ceria particles by a solid phase displacement reaction will be described more specifically. First, a cerium salt, which is a precursor, is calcined in air to generate ceria particles by a substitution reaction with oxygen. Then, it is pulverized mechanically to a predetermined size to produce dry ceria particles. Examples of the cerium salt serving as a precursor include cerium (III) carbonate, cerium (III) oxalate, and cerium (III) acetate. Among them, cerium (III) carbonate is preferably used in terms of ease of use. Is done. The firing temperature is preferably 600 ° C. or higher, more preferably 700 ° C. or higher. The firing time is preferably 3 hours or more, and more preferably 4 hours or more. When the firing temperature is 600 ° C. or higher, the substitution reaction proceeds sufficiently. If the firing time is 3 hours or longer, crystallization proceeds sufficiently, and the polishing performance is improved. The method of pulverizing the dry ceria particles generated by firing is not particularly limited as long as it can be pulverized to a predetermined size. Is preferably used. The dry ceria produced in this way has a high polishing efficiency because it has an irregular crystal shape as shown in FIG.

  Next, a method for polishing a synthetic quartz glass substrate using the abrasive of the present invention will be described. Since the abrasive of the present invention is particularly preferably used in the finish polishing step after the rough polishing step, a case where single-side polishing is performed in the finish polishing step will be described as an example. However, the abrasive is of course not limited to this, and the abrasive of the present invention can also be used for rough polishing. The abrasive of the present invention can be used not only for single-side polishing but also for double-side polishing.

  A single-side polishing apparatus that can be used in the polishing method of the present invention includes, for example, as shown in FIG. Polished single-side polishing apparatus 10. Further, as shown in FIG. 3, the polishing head 2 can hold the synthetic quartz glass substrate W to be polished, and can rotate. The platen 3 can also rotate. As the polishing pad 4, nonwoven fabric, foamed polyurethane, porous resin, or the like can be used. Further, it is preferable that the surface of the polishing pad 4 is always covered with the abrasive 1 during the polishing, and therefore, by providing a pump or the like to the abrasive supply mechanism 5, the polishing agent is continuously provided. It is preferred to supply 1.

  In such a single-side polishing apparatus 10, the synthetic quartz glass substrate W is held by the polishing head 2, and the polishing agent 1 of the present invention is supplied onto the polishing pad 4 from the polishing agent supply mechanism 5. Then, polishing is performed by rotating the surface plate 3 and the polishing head 2 to bring the surface of the synthetic quartz glass substrate W into sliding contact with the polishing pad 4. With such a polishing method using the abrasive of the present invention, the polishing rate can be increased and the generation of defects due to polishing can be suppressed. In addition, the polishing method of the present invention can obtain a synthetic quartz glass substrate having significantly less defects, and thus can be suitably used for finish polishing.

  In particular, the synthetic quartz glass substrate that has been subjected to finish polishing by the polishing method of the present invention can be used for semiconductor-related electronic materials, and can be suitably used for photomasks, nanoimprints, and magnetic devices. The synthetic quartz glass substrate before the finish polishing can be prepared, for example, by the following steps. First, a synthetic quartz glass ingot is formed, and thereafter, the synthetic quartz glass ingot is annealed, and then, the synthetic quartz glass ingot is sliced into a wafer. Subsequently, the sliced wafer is chamfered, then wrapped, and subsequently polished to mirror-finish the surface of the wafer. Then, the synthetic quartz glass substrate thus prepared can be subjected to finish polishing by the polishing method of the present invention.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples.

(Example 1)
First, an abrasive for a synthetic quartz glass substrate was manufactured as follows.

(Synthesis of wet ceria)
A solution of 1000 g of cerium (III) nitrate hexahydrate (Ce (NO ₃ ) ₃ .6H ₂ O) dissolved in 250 g of pure water was mixed with 100 g of nitric acid to obtain a cerium (III) solution. Next, 1 g of diammonium cerium nitrate ((NH ₄ ) ₂ Ce (NO ₃ ) ₃ ) was dissolved in 500 g of pure water to obtain a cerium (IV) solution. Subsequently, the cerium (III) solution and the cerium (IV) solution were mixed to obtain a cerium mixed solution.

  4000 g of pure water was dropped into the reaction vessel under a nitrogen gas atmosphere, and then 1000 g of ammonia water was dropped into the reaction vessel, followed by stirring to obtain a basic solution.

  Next, the cerium mixed solution was dropped into the reaction vessel, stirred, and heated to 80 ° C. in a nitrogen gas atmosphere. Heat treatment was performed for 8 hours to obtain a mixed solution containing ceria particles.

  After cooling the mixture containing the ceria particles to room temperature, nitric acid was added dropwise to the mixture to adjust the pH of the mixture to an acidity of 2 or less, thereby terminating the reaction. After sedimentation of the ceria particles in the mixture, washing and centrifugation were repeated several times with pure water, and finally wet ceria particles were obtained. The average primary particle diameter of the wet ceria particles measured by an electron microscope was 60 nm.

(Synthesis of dry ceria)
500 g of cerium (III) carbonate octahydrate (Ce ₂ (CO ₃ ) ₃ .8H ₂ O) is put into a rotary kiln, dried at 120 ° C. for 30 minutes, and then at 800 ° C. in the air for 4 hours. A baking treatment was performed to obtain ceria particles. The obtained ceria particles were put into a pulverizer and pulverized for 15 hours to finally obtain dry ceria particles. The average primary particle diameter of the dry ceria particles measured by an electron microscope was 200 nm.

(Preparation of abrasive for synthetic quartz glass substrate)
350 g of wet ceria particles having an average particle diameter of 60 nm synthesized by the above method, 150 g of dry ceria particles having an average particle diameter of 200 nm, 5 g of sodium polyacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) as an additive, and 5000 g of water was mixed, and ultrasonic dispersion was performed for 60 minutes while stirring. The obtained slurry was filtered with a 0.5-micron filter and diluted with pure water to obtain an abrasive for a synthetic quartz glass substrate. The abrasive for a synthetic quartz glass substrate has a wet ceria particle / dry ceria particle mass ratio of 70/30, a mixed abrasive particle concentration of 10% by mass, and an additive (sodium polyacrylate) concentration of 0.1% by mass. , PH was 5.6. Further, 1 part by mass of the additive was contained with respect to 100 parts by mass of the mixed abrasive particles.

(Example 2)
An abrasive was prepared in the same procedure as in Example 1 except that the mixed abrasive particles were 400 g of wet ceria particles having an average particle diameter of 60 nm and 100 g of dry ceria particles having an average particle diameter of 200 nm (mass ratio: 80/20). did. The pH of the obtained abrasive was 5.6.

(Example 3)
An abrasive was prepared in the same procedure as in Example 1 except that the mixed abrasive particles were 450 g of wet ceria particles having an average particle diameter of 60 nm and 50 g (mass ratio: 90/10) of dry ceria particles having an average particle diameter of 200 nm. . The pH of the obtained abrasive was 5.8.

(Example 4)
An abrasive was prepared by the same procedure as in Example 1, except that wet ceria particles having an average particle diameter of 20 nm and dry ceria particles having an average particle diameter of 200 nm were mixed at a mass ratio of 70/30 to produce mixed abrasive particles. . The pH of the obtained abrasive was 5.5. Hereinafter, the average particle diameter of the wet ceria particles was changed by adjusting the mixing ratio of the cerium (III) solution and the cerium (IV) solution. The average particle size of the dry ceria particles was adjusted by changing the pulverization time by a pulverizer.

(Example 5)
An abrasive was prepared in the same procedure as in Example 1 except that wet ceria particles having an average particle diameter of 60 nm and dry ceria particles having an average particle diameter of 80 nm were mixed at a mass ratio of 70/30 to produce mixed abrasive particles. . The pH of the obtained abrasive was 5.5.

(Example 6)
An abrasive was prepared by the same procedure as in Example 1 except that wet ceria particles having an average particle diameter of 60 nm and dry ceria particles having an average particle diameter of 500 nm were mixed at a mass ratio of 70/30 to produce mixed abrasive particles. . The pH of the obtained abrasive was 5.5.

(Example 7)
A ceria abrasive was prepared in the same procedure as in Example 1, except that wet ceria particles having an average particle diameter of 20 nm and dry ceria particles having an average particle diameter of 80 nm were mixed at a mass ratio of 70/30 to produce mixed abrasive particles. did. The pH of the obtained ceria abrasive was 5.5.

(Comparative Example 1)
An abrasive was prepared in the same procedure as in Example 1 except that the mixed abrasive particles were 250 g of wet ceria particles having an average particle diameter of 60 nm and 250 g of dry ceria particles having an average particle diameter of 200 nm (mass ratio: 50/50). . The pH of the obtained abrasive was 5.1.

(Comparative Example 2)
An abrasive was prepared in the same procedure as in Example 1, except that the mixed abrasive particles were 50 g of wet ceria particles having an average particle diameter of 60 nm and 450 g of dry ceria particles having an average particle diameter of 200 nm (mass ratio: 10/90). . The pH of the obtained abrasive was 5.6.

(Comparative Example 3)
An abrasive was prepared in the same procedure as in Example 1 except that dry ceria particles were not mixed and only wet ceria particles were used as abrasive particles. The pH of the obtained abrasive was 5.1. The average particle size of the wet ceria particles was 60 nm.

(Comparative Example 4)
An abrasive was prepared in the same procedure as in Example 1, except that wet ceria particles were not mixed and only dry ceria particles were used as abrasive particles. The pH of the obtained abrasive was 5.2. The average particle size of the dry ceria particles measured by an electron microscope was 200 nm.

  Using the polishing agents prepared in Examples 1 to 7 and Comparative Examples 1 to 4, a synthetic quartz glass substrate was set in a polishing apparatus and polished. The polishing conditions are as follows.

(Polishing conditions)
First, a synthetic quartz glass substrate having a diameter of 4 inches (100 mm) after performing rough polishing on a polishing head was set. Then, while supplying the polishing agent to the polishing pad attached to the surface plate, the synthetic quartz substrate held by the polishing head is brought into sliding contact with the polishing pad, and an amount sufficient to remove defects generated in the rough polishing step. Was polished on one side by 2 μm or more. As the polishing pad, a soft suede type polishing pad (manufactured by FILWEL Corporation) was used. The polishing load was 60 gf / cm ² , the rotation speed of the platen and the head was 50 rpm, and the supply amount of the abrasive was 100 ml per minute.

  The polished synthetic quartz glass substrate was removed from the head, washed with pure water, and further subjected to ultrasonic cleaning. Thereafter, the synthetic quartz glass substrate was dried at a temperature of 80 ° C. in a dryer.

  Next, the polishing rate was calculated by measuring the change in the thickness of the synthetic quartz glass substrate before and after polishing with a reflection spectral film thickness meter (SF-3 manufactured by Otsuka Electronics Co., Ltd.). Further, the number of defects having a size of 100 nm or more, which occurred on the surface of the polished synthetic glass substrate, was determined by a laser microscope.

  Table 1 shows the results. The numbers in Table 1 are the average values of five polished synthetic quartz glass substrates.

  Using the abrasives of Examples 1 to 7, ie, mixed abrasive particles obtained by mixing wet ceria particles and dry ceria particles in a mass ratio of 70/30 or more and 90/10 or less as abrasive grains, synthetic quartz By polishing the glass substrate, it was possible to suppress the occurrence of defects due to the polishing, and to obtain a high polishing rate.

  In Examples 1 to 3, the average primary particle diameter of wet ceria particles is 40 nm or more and 100 nm or less, and the average primary particle diameter of dry ceria particles is 100 nm or more and 300 nm or less. Therefore, Examples 1 to 3 were compared with Examples 4 and 7 in which the average primary particle diameter of the wet ceria particles was less than 40 nm and Example 5 in which the average primary particle diameter of the dry ceria particles was less than 100 nm. A high polishing rate could be obtained. Further, in Examples 1 to 3, defects could be reduced as compared with Example 6 in which the average primary particle diameter of dry ceria particles was larger than 300 nm.

  On the other hand, the abrasives of Comparative Examples 1 and 2 in which the mixing ratio of dry ceria particles is higher than that in the examples, the polishing rate for the synthetic quartz glass substrate is high because the ratio of wet ceria particles is low, but the generation of defects is large. The result was. In addition, the polishing agent of Comparative Example 3 used only wet ceria particles as abrasive grains, so that the number of occurrences of defects was somewhat smaller than that of Example, but the polishing rate was lower than that of Example. Inferior results. Conversely, the polishing agent of Comparative Example 4 used only dry ceria particles as the abrasive grains, so that the polishing rate for the synthetic quartz glass substrate was higher than that of the Example, but the polishing rate of the synthetic quartz after polishing was higher. The number of defects generated on the surface of the glass substrate was much larger than that of the example.

  Note that the present invention is not limited to the above embodiment. The above embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and has the same effect. Within the technical scope of

Claims (9)

A synthetic silica glass substrate abrasive containing abrasive particles and water,
The abrasive particles are made of mixed abrasive particles of wet ceria particles and dry ceria particles, and the mass ratio of the wet ceria particles to the dry ceria particles is 70/30 or more and 90/10 or less. Abrasive for synthetic quartz glass substrates.   The synthetic silica glass substrate according to claim 1, wherein the average primary particle diameter of the wet ceria particles is 40 nm or more and 100 nm or less, and the average primary particle diameter of the dry ceria particles is 100 nm or more and 300 nm or less. Abrasive.   The concentration of the mixed abrasive particles is 5 parts by mass or more and 40 parts by mass or less based on 100 parts by mass of the abrasive for a synthetic quartz glass substrate. Abrasive for synthetic quartz glass substrates.   4. The method according to claim 1, further comprising an additive, wherein the additive has a concentration of 0.1 to 5 parts by mass based on 100 parts by mass of the mixed abrasive particles. The abrasive for a synthetic quartz glass substrate according to claim 1 or 2.   The abrasive for a synthetic quartz glass substrate according to any one of claims 1 to 4, wherein the pH is 3.0 or more and 8.0 or less. A method for polishing a synthetic quartz glass substrate having a rough polishing step and a finish polishing step after the rough polishing step,
A method for polishing a synthetic quartz glass substrate, comprising: performing the finish polishing using the abrasive for a synthetic quartz glass substrate according to any one of claims 1 to 5 in the finish polishing step. A method for producing an abrasive for a synthetic quartz glass substrate,
Producing wet ceria particles,
A step of producing dry ceria particles,
Mixing the wet ceria particles, the wet ceria particles and water such that the mass ratio of the wet ceria particles to the dry ceria particles is 70/30 or more and 90/10 or less. A method for producing an abrasive for a synthetic quartz glass substrate.   In the wet ceria particle producing step, a mixed solution is prepared by mixing a cerium salt and a basic solution, and the wet ceria particles are produced by a wet chemical precipitation reaction by heating the mixed solution. The method for producing an abrasive for a synthetic quartz glass substrate according to claim 7.   9. The synthetic quartz glass substrate according to claim 7, wherein, in the dry ceria particle manufacturing step, the dry ceria particles are manufactured by a solid-phase substitution reaction by firing a cerium salt in the presence of oxygen. 10. Method for manufacturing abrasives.